Right now the OS icons are ordered Linux, Windows, and OS X. For the most part, the ordering of OS' has always been Windows, OS X, and Linux. This is true of Steam, GOG.com (sans Linux), Desura, most pages on this wiki, and the Humble Bundle pages themselves. This is also usually true of the release order per operating system. While this a minor detail, I think it would be preferable to order it in the most common way. We should be able to change this with a simple "Find and Replace All".
Topic on Talk:Humble Bundle
Well, this order does one thing nicely, and that's keeping the Windows icon in a single column across the whole page. I find that highly preferable, and I'm sure no one is confused by the order being different than on other services or other pages on the wiki.
I have changed the OS order for this page as well as Humble Store.